Been for a fly this morning and experimented with how the setup works.
I found out that the usb supply is actually on the main bus not the avionics, so turning on the pilotaware before the engine is actually possible, it just takes a long while of waiting with the master switch on before being able to start the engine.

I might just revert to battery power for the pilotaware as I already have the battery and it easily lasts a full days flying.